Means for the underground storage of liquified gas

ABSTRACT

Liquified gas is stored underground in a large double walled container seated in an opening in the earth&#39;&#39;s surface. Between the walls of the liner, thermal insulation is distributed in a continuous layer along the floor and wall of the opening. A diaphragm is supported across the top of the opening with a seal being provided between the diaphragm and the double walled liner to form a container for the liquified gas. Surrounding the lip of the opening is a concrete ring across which a net of cables is stretched to support a thermally insulating ceiling. A cooling system is provided for freezing the earth to aid in the excavation of the opening and this system is subsequently used to maintain the wall and floor of the opening frozen to a controlled thickness by cooling them in response to a rise in the temperature of the surrounding earth above a predetermined temperature level. Also disclosed are various techniques for constructing a storage tank of the type described.

Connell et a1.

Oct. 31, 1972 [S4] MEANS FOR THE UNDERGROUND STORAGE OF LlQUlFlED GAS[72] inventors: Joseph A. Connell, Harbor City; Anthony J. Baranyi,Costa Mesa, both of Calif.

[73] Assignee: Systems Capital Corporation,

Phoenix, Ariz.

[22] Filed: Oct. 12, 1970 [21] Appl.No.: 79,980

[52] U.S.Cl. ..62/45,61/0.5,52/269 [51] lnt.C1. ..F17c7/02 [58] Field ofSearch ..62/45;61/0.5;252/269 [56] References Cited UNITED STATESPATENTS 3,196,622 7/1965 Smith et al ..62/45 3,300,982 1/1967 Meade..6l/0.5 3,326,011 6/1967 Sparling ..62/45 3,360,941 1/1968 Jackson..61/0.5 3,379,012 4/1968 Jackson ..6l/0.5 3,418,812 12/1968 Khan et a1...61/0.5 3,516,568 6/1970 Fish ..61/0.5 X

OTHER PUBLlCATlONS P. E. Glaser, Effective Thermal Insulation:Multilayer Systems Cryogenic Engineering News, April, 1969, pps. 16through 24.

Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C. CaposselaAttorney-Fowler, Knobbe & Martens [57] ABSTRACT Liquified gas is storedunderground in a large double walled container seated in an opening inthe earth's surface. Between the walls of the liner, thermal insulationis distributed in a continuous layer along the floor and wall of theopening. A diaphragm is supported across the top of the opening with aseal being provided between the diaphragm and the double walled liner toform a container for the liquified gas. Surrounding the lip of theopening is a concrete ring across which a net of cables is stretched tosupport a thermally insulating ceiling. A cooling system is provided forfreezing the earth to aid in the excavation of the opening and thissystem is subsequently used to maintain the wall and floor of theopening frozen to a controlled thickness by cooling them in response toa rise in the temperature of the surrounding earth above a predeterminedtemperature level.

16 Claims, 10 Drawing Figures MEANS FOR THE UNDERGROUND STORAGE OFLIQUIFIED GAS The present invention relates to the storing of largequantities of liquified gas, most advantageously natural gas and inparticular to the storing of such liquified gas underground.

Three difi'erent concepts have been utilized in existing cryogenicliquified gas storage systems. These concepts have respectively involvedthe use of above ground tanks, below ground tanks, and in groundstorage. Above ground tanks are generally constructed with a double wallhaving insulation between the inner and outer walls. The inner tank isconstructed of a material capable of withstanding cryogenictemperatures. Such materials include aluminum, stainless steel, 9percent nickel steel and reinforcing concrete. The outer tank may bemade of carbon steel since the insulation protects it from the cryogenictemperatures.

Above ground tanks have several disadvantages. First, they are expensiveto construct. Secondly, they require a diked area around the tank tocontain the liquid in the event of tank failure, necessitating the useof additional land. Thirdly, in many urban and suburban areas, aboveground tanks are not permitted because of their appearance.

To overcome the disadvantages of above ground tanks, several methods ofconstructing below ground tanks have been attempted. Most of theseinvolve the us of a concrete tank submerged wholly or partially in theground. In a few cases metal tanks have been so used. in several cases avoid was left between the below ground tank and the surrounding earthand this void was then filled with insulating material. Below groundtanks also suffer from the disadvantage of being expensive.Additionally, since the submerged tanks are rigid structures, steps mustbe taken to safeguard against frost heaving by the surrounding earthwhich might cause the tank to rupture.

The above problems have lead to several attempts to store liquifiedgases and particularly liquid natural gas in a frozen hole in theground. In most of these cases, the earth itself has been the liquidcontainer, while in a few instances a flexible moisture-impervious linerhas been incorporated. Although the heat leak into these tanks isusually excessive, a few of them have enjoyed success. A principalproblem with this approach is that the success or failure of the projectdepends almost entirely on the effect that cryogenic temperatures haveon the soil and rock formation in which the container is constructed. Inseveral cases, subjecting the soil and rock to cryogenic temperatureshas resulted in fracture and fissure formations which increased heatleak to the point where the tank was not useable and had to beabandoned.

The present invention is directed to achieving the advantages ofunderground storage, such as a lower profile and a lower cost, whileavoiding the past problems of this approach, such as damage to the tankwalls by frost heaving. In accordance with the present invention, a tankis constructed in the ground either in an existing hole or, ifnecessary, in a specially excavated opening. Preferably, the excavationis accomplished by the known technique of freezing an earthen wallaround the area which is to be excavated and then excavating theunfrozen center.

A principal reason for selecting ground freezing as an aid in excavationis to permit the use of vertical side walls without the need for piling.

In accordance with a particular feature of the present invention, groundfreezing is used for more than a mere aid in excavation. The frozen ringaround the excavated opening is maintained as a permanent structuralsupport for the tank. Additionally, after the hole has been dug, itsfloor may also be frozen and maintained frozen by means of a heatexchanger buried in the floor of the opening. in this manner, a frozenshell of earth is provided around the storage tank for stable structuralsupport.

Inside the opening a double walled, thermally heavily insulatedcontainer is installed. The container is comprised principally of anouter liner of moisture-impervious material whose size and shape aresuch as to conform to the wall and floor of the opening. Inside thisliner, stacked upon the floor and wall of the opening are cryogenicallystable, porous bags filled with thermal insulation, such as Perlite. Asecond bucket-shaped liner is installed inside the thermal insulationand is sealed at its top to the outer liner. Preferably, both liners aresuspended from a concrete ring which surrounds the lip of the openingand which is installed prior to its excavation. The container is cappedby a diaphragm which is suspended from the concrete ring, and athermally insulating ceiling is installed above the diaphragm, thisceiling also being preferably supported by the concrete ring.

The above described structural features have several importantadvantages. Among these is the fact that the container structure insidethe opening is relatively inexpensive when compared with a solid shellof concrete or metal. Moreover, since the container is highly flexible,it is less susceptible to leakage due to fracture. The packing ofthermal insulation into bags of cryogenieally stable porous materialinsures that the thermal insulation will not be crushed or ruptured whenthe container is filled with liquified gas. This has tended to be aproblem in several previously conceived in-ground tanks in which thermalinsulation was formed by pouring a formed wall of polyurethane or someother form of insulating material. This material, when subjected tocryogenic temperatures, tends to contract, causing the insulation topull away from the earthen wall of the opening and to be crushed by theweight of the stored liquid in the container pressing against theinsulation. Moreover, by using a porous material for the bags, theproblem of air escaping from the bag as the bag is compressed by theweight of insulation above it as well as by the weight of the liquid inthe tank is eliminated. Another advantage of the proposed constructionof the double walled container is that the air initially capturedbetween its walls may be replaced either by a vacuum or by an inert gas,thereby retarding the deterioration of the insulation.

Another feature of the subject invention is that the thickness of thefrozen shell of earth around the container of liquified gas ismaintained within predetermined limits. This is achieved by the use of aset of temperature sensors installed into the ground around the openingto some distance from its frozen wall and also underneath the floor ofthe opening. Temperature sensors and freeze pipes are installed aroundthe opening at the same time. Additional temperature sensors areinstalled along the inner wall and base of the opening after itsexcavation is complete. The sensors are used to control a cooling systemconnected to the freeze pipes and, by either automatic control mans orthrough manual adjustments, the output of the cooling system is modifiedin response to the readings obtained from the temperature sensors.Toward this end, the thermal insulation which is between the inner andouter liners of the container is made sufficiently thick so that theheat loss from the earthen shell surrounding the opening into thecontainer of liquified gas is not enough to maintain the earth aroundthe opening frozen to any substantial distance. Rather, the storage tankis so designed that it is necessary to run the cooling system in orderto maintain the wall and floor of the opening frozen to a desireddistance. This feature of the invention tends to prevent ice lenses fromforming around the opening and lifting or shifting the entire tank.

By using a separate cooling system to maintain a frozen earthen shellaround the container of liquified gas the rate of heat flow from theearth into the container is reduced below the level which would exist ifonly the insulation were relied upon for this purpose. This in turnreduces the boil-off rate of the liquified gas in the container to adesirably low level.

The unique insulating system of the present invention is useful,however, even if the opening in which the container is retained is notsurrounded by frozen earth but is instead in a solid rock formation,because it serves to insulate the rock formation from the lowtemperature of the liquified gas being stored, thereby avoiding theproblem of fracture and fissure formation which has plagued in-groundtanks in the past.

The present invention and its advantages will be more clearly understoodwith reference to the following description of a preferred embodimentthereof taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view, partially cut away, of a storage tankincorporating features of the present invention;

FIG. 2 is a cross-section along line 2-2 of the storage tank illustratedin FIG. 1;

FIG. 3 is a sectional view of a wall of the storage tank illustrated inFIG. 2, taken along line 3-3;

FIG. 4 is a sectional view of the ceiling and roof of the storage tankillustrated in FIG. 2, taken through line 4-4;

FIG. 5 is an enlarged sectional view of the supporting concrete ringsurrounding the mouth of the opening which houses the storage tankillustrated in FIG. 2;

FIG. 5a is an enlarged perspective cross-sectional view of a portion ofthe concrete ring of FIG. 5 showing more clearly the manner in which theseveral layers of the storage tank are anchored upon the ring;

FIG. 6 is a sectional view of the floor of the storage tank of FIG. 2,taken through line 6-6;

FIG. 7 is an enlargement of a portion of FIG. 2 to illustrate some ofthe details of the submerged pump used in the illustrated storage tankand the manner in which it is installed therein;

FIG. 8 is a side view of a few of the freeze pipes which are sunk intothe earth in a circular array and through which a refrigerant is pumpedto create a frozen shell of earth to provide structural support for thestorage tank of FIGS. 1 and 2; and

FIG. 9 is a block diagram illustrating a cooling system for initiallyfreezing the floor and walls of the opening and for maintaining themfrozen to a constant thickness.

An underground storage tank incorporating features of the presentinvention is illustrated in FIGS. 1, 2, and 5. It is comprisedprincipally of an opening 13 in the earth's surface housing a doublewalled container 15. The container is shown to be fabricated of abucketshaped inner liner l7 capped by a diaphragm 19. The inner liner 17of the container is surrounded by insulating pillows 21 comprised ofthermal insulation packed in bags, and the pillows 21 are in turn heldwithin an outer bucket-shaped liner 23 which serves to prevent moisturefrom the earth from seeping into the thermal insulation. A concrete ring25 surrounds the lip of the opening 13 and serves as a structuralsupport for the ceiling 27. The latter includes a net 29 of cables uponwhich several layers of thermally insulating pillows 31, typically bagspacked with thermal insulation are distributed. If desired, a roof 33supported by an inert gas such as nitrogen may be anchored upon the ring25 to prevent damage to the ceiling 27. Cryogenic fluid is pumped out ofthe storage tank by a submersible pumping system 37 which is suspendedinto the storage tank from a cantilever support structure 35.

As mentioned previously, the storage tank of the present invention maybe either in an opening which is in a rock formation, in which casefreezing of the ground is not required, or it may be formed in anopening in soil in which case it is desirable that the ground be frozenboth as an aid in construction and to provide structural strength duringoperation of the tank. The tank which is illustrated in the FIGURES isof the latter type. The first step in constructing the subject storagetank is to investigate the soil conditions at the site thoroughly. Theresults of this investigation will help determine the exact constructionmethods which are to be employed, the required thickness of the soilthat is to be frozen, as well as the amount of refrigeration that willbe required.

The first step in ground freezing is the insertion of freeze pipes intothe ground on a circle which will ultimately be the center of the frozenearthen wall. Pipes 39 and 41 which are alternately long and short, asillustrated in FIG. 8, are preferably employed, with the long pipes 39extending into the ground about l0-20 percent deeper than the bottom ofthe ultimate excavated hole. The short pipes 41 extend into the groundapproximately 20 feet. The staggered arrangement of pipes provides agreater transfer surface and hence cooling capacity near the groundlevel where the largest amount of heat must be removed from the soil. Inorder to permit close control of the rate of freezing, two separatesystems 43 and 45 for circulating refrigerant through the pipes areshown. The first system 43 is connected to the long pipes 39 through amanifold 44 and the second system 45 is connected to the short pipes 41through a second manifold 46. The advantage of this arrangement derivesfrom the fact that at times during normal tank operation heat leak fromthe ground into the insulated tank is not sufficient to maintain thefrozen wall at the desired thickness. When this occurs, it is onlynecessary to pass refrigerant through the short pipes 41 since it isfrom the ground surface that the heat leak into the tank is thegreatest.

As shown in FIG. 2, the long freeze pipes 39 are comprised of coaxialpipes 39a and 39b, and the manifold 44 is comprised of an inlet manifold44a and a return manifold 44b. Refrigerant is circulated from thecooling unit 43 down through the inside freeze pipes 39a, up through theoutside freeze pipes 39b and back to the cooling unit 43 through thereturn manifold 44b. The short pipes 41 and their associated manifold 46are similarly constructed.

At the same time that the freeze pipes 39 and 41 are installed, severalrows of temperature sensors 47, preferably of the type which produce anelectrical indication of temperature on a pair of wires, are alsoinserted into the ground on radii extending out from the tank. Thesensors may be contained in pipes (not shown), sunk into the earth tothe same length as the long freeze pipes 39, and containing temperaturesensors throughout their length. The wires of the sensors will, ofcourse, be brought up through the pipes for connection to suitablecontrols or indicators. By sensing and monitoring the groundtemperatures with the temperature sensors 49, the progress of groundfreezing may be monitored and the time when excavation may begin can bedetermined. The temperature sensors 49 in combination with additionalsensors 49 and 50 which are inserted inside the excavation l3 and alsobeneath its floor also serve to monitor the temperature of the earthsurrounding the excavation during operation of the tank, as will beexplained in greater detail hereinafter.

After the walls have been frozen to the desired thickness, excavation ofthe unfrozen center of the frozen ring by any of several known methodsmay begin. After excavation has progressed to a depth which willrepresent the bottom of the concrete ring 25, the latter is installed.The ring 25 contains reinforcing steel rods whose number and thicknesswill depend upon the diameter of the opening and upon the loads whichthe ring is to carry. The necessary calculations for determining thenumber, thickness and distribution of the reinforcing steel rods arewell known in the civil engineering art and will not be describedherein. It might be noted that, before the concrete ring 25 is poured,it is desirable that some portion of the frozen earth be chipped out inorder that the concrete may be poured directly against the frozen groundto eliminate the possibility of ice lens formation.

After the concrete ring 25 has been installed, the unfrozen earth withinis excavated to a depth which is several feet greater than thatultimately required. In the over-excavated portion at the bottom a heatexchanger 51 consisting of a series of connected pipes is installed. Theheat exchanger 51 is connected to the manifold 44 which serves the longpipes 39. Additional temperature sensors 49 and 50 are placed along thebottom of the opening and along its side. After the heat exchanger 51and the additional temperature probes 49 have been installed on thebottom of the opening 13, they are covered with a layer of sand 52 to adepth of several feet, usually less than four. Refrigerant is thenpumped through the heat exchanger 51 until a bottom which is typicallyfour feet thick is frozen.

The installation of the tank may now begin. First, the wall of theopening 13 is smoothed, preferably by spraying water upon it whichfreezes and produces a smooth surface. To further insure that no damagewill be done to the outer liner 23, padding is installed all around theopening over its wall and over its floor. This may be done by fiberglassmats 53 in the form of vertically running strips attached to the wall ofthe opening and layed over its floor, as shown in H65. 3 and 6. Afterthe mats 53, which should be at least an inch thick, have beeninstalled, the outer liner 23 is lowered into the opening. Preferably,it will be prefabricated to have a shape which conforms to the shape ofthe opening 13 and to have a size which is slightly larger than theopening. The latter will insure that when the outer liner 23 is put inplace it will be slightly wrinkled so as to preclude the possibility ofits being placed in tension when the tank is filled.

The outer liner 23 should be made of a cryogenically stable material.One which is believed will be found suitable includes at least onemultilayer laminate having layers of aluminum and polyester. At its topthe outer liner 23 is provided with a radially extending flange 23a bywhich it is anchored to the concrete ring 25. For this purpose aplurality of bolts 55 are anchored around the periphery of the concretering 25 and the rim 23a is fastened upon these bolts. FIGS. 5 and 5ashow a suitable arrangement wherein the bolts 55 are distributed aroundthe periphery of the concrete ring in a channel 58. A sealant paste isfirst applied in a layer 60 to the bottom of the channel 58 around thebolts 55, and the outer liner flange 23a is placed on top of the sealantlayer 60. At subsequent stages of construction the extreme portions ofthe screening 61 and of the inner liner 17 are also extended into thechannel 58, with additional layers 62 and 64 of sealant being appliedunder each of them. Finally, the entire sandwich structure thus formedis clamped by means of a series of arcuate retaining strips 56 made of adurable cryogenically stable material. The strips 56 will be typicallyseveral feet long and will be predrilled to mate with approximately sixbolts 55 for each strip, each bolt receiving a respective nut 66 tosecure the strips 56 thereon.

Having installed the outer liner 23, the thermal insulation may now beinstalled upon the floor of the opening on top of the liner. inaccordance with a feature of the invention, the insulation is in theform of pillows 21 wherein particulated insulation is packed in bags 57made of a cryogenically stable, porous material. The material needs tobe cryogenically stable since at least some of the bags will be exposedto the cryogenic ternperatures of the liquid stored within the tank. Theadvantage of making the bags out of porous material is that this allowstrapped air to escape from within the bags when the tank is filled.Perlite has been found to be suitable for the insulating material.

The number of layers of insulating pillows 21 are a matter of choice,three being shown in the drawings.

Once the floor of the opening has been covered with the desired numberof layers of bagged thermal insulation, the insulating of the wall ofthe opening 13 within the outer liner 23 may begin. The use ofinsulating pillows 21 comprised of bagged Perlite is again preferred.The insulating of the wall of the opening is best achieved by firststacking insulating pillows 21 along the wall of the opening 13 to amoderate height such as for example 10 feet. To prevent the inner liner17 from having a sharp corner and thereby to reduce the chances ofrupture when the tank is filled it is desirable at this point to installall around the bottom corner of the opening 13 next to the pillows 21 aseries of triangularly cross-sectioned corner pillows 65 which may becomprised of the same materials as those used for the pillows 21.

Means are next installed to help retain the insulating pillows 21 whichhave been stacked next to the wall of the opening. In the exemplaryembodiment illustrated in FIGS. 1 and 2, these means comprise ascreening 61 combined with a series of expandable retaining bands 59. Asbest seen in FIG. 1, the screening 61 is made up of a plurality ofscreen strips 63 which are laid upon the floor of the opening, withtheir edges slightly overlapping to make for a continuous, pie-shapedpiece of screening. The screen strips 63 are brought up next to thestacked pillows along the wall of the opening 13. To hold the screenstrips 63 in place against the bags 21 a first retaining band 59 isinstalled and is expanded sufficiently to hold it, and the screen strips63 in place. The retaining bands are provided for this purpose with oneor more ratcheted expanding joints 60 of conventional construction whichpermit the retaining bands to expand, both during installation andsubsequently, when the bands are further expanded typically by severalfeet, by the pressure exerted upon them when the storage tank is filled.The retaining bands will generally be of a semitubular shape, that istheir cross-section would be arcuate, to obtain structural strength andto present a smooth surface without abrupt corners to the inner liner17. The ratcheted expanding joints 60 would be in the hollow of theretaining bands and would have no contact with inner liner 17. Theratcheting is so arranged that the retaining bands 59 can only expandand cannot contract even when the pressure which had caused them toexpand in the first place is removed, as by emptying of the storagetank.

The screen strips 63 overlap not only along the floor of the opening,but also along the wall so that a generally cylindrical screening isformed inside the insulating pillows 21 along the wall of the opening.in some instances it may be advisable to sandwich a lubricant, such as astrip of polyester, between the overlapping edges of adjacent screenstrip 63 so as to allow them to slide rather than tearing in response tothe pressure of liquid within the tank.

Once the screen strips 63 have been fastened under the first retainingband 59, more insulating pillows 21 may be piled on top of those whichhad been initially placed next to the wall. As shown in FIG. 2 when thepillows 21 have been stacked along the wall to an additional height,approximately the same as the initial height of pillows stacked there,another retaining band 59 is installed and the screen strips 63 areraised all around the wall of insulation and fastened under the secondretaining band 59. This process continues, with additional pillows beingpiled on top of those stacked previously and with successive retainingbands 59 being installed, each time raising the screen strips just abovethe last retaining band so installed. The process continues until thewall of insulating pillows and the screening 61 inside it reaches thetop of the opening 13. At this point the screen strips 63 are broughtover on top of the pillows 21 and are fastened upon the concrete ring 25in the manner explained previously with reference to FIG. 5a.

The next step is to install the inner liner 17 which in the preferredembodiment has the same bucket shape as the outer liner 23, but which ofcourse is made to be smaller. The inner liner 17 is provided with aradially extending flange 17a at its top and the flange is fastened ontop of the outer liner flange 230 by means of the bolts 55 and thewashers 56 (HO. 5a).

As an aid in the proper installation of the inner liner 17 the airbetween the inner and outer liners l7 and 23 is exhausted through anopening 69. The resulting vacuum inside the space formed by the twoliners 17 and 23 causes the inner liner 17 to press against thescreening 61 so that both the screening and the inner liner conformgenerally to the shape of the pillows 21 which are stacked against thewall of the opening. The inner liner 17 is designed with a waffledsurface con figuration to be slightly larger than the space inside theinsulating pillows 21.

It may be seen at this point that the screening 61 serves a dualpurpose. As noted earlier, it serves to hold the insulating pillows 21flat against the wall of the opening in combination with the retainingrings 59. The screening 61 also serves, however, as a reinforcement forthe inner liner 17. Thus where the liner bridges a gap between adjacentinsulating pillows, and particularly where such a bag collapses underthe weight of cryogenic liquid within the inner liner 17, the screeningkeeps the inner liner from ballooning into the resulting space. For thisreason, the screening is preferably made of some cryogenically stablematerial having good structural strength. It may be, for example, madeof either fiberglass screening, aluminum screening, or stainless steelscreening. Tests have proven that the strength of the laminate whichmakes up the inner liner 17 can be substantially increased by use of thescreening 61. It should be understood that the concept of a storage tankwherein screening and retaining bands are used to support the insulatingwall pillows 21 and to reinforce the inner liner 17 is not claimedherein since it is the joint invention of Joseph A. Connell, Anthony J.Baranyi and Paul V. Laylander. lnstead, it is claimed in a separateapplication entitled Cryogenic Storage Tank lmprovements, Ser. No.80,117 being filed Oct. l2, 1970 by the said inventors. It should alsobe understood that, while the use of screening and retaining bands toretain the insulating wall pillows 21 has significant advantages, theiruse is not essential to construct a storage tank incorporating the basicconcepts of the present invention. Other means for retaining theinsulating pillows may occur to those skilled in the art and these meansmay or may not serve also to reinforce the inner liner 17.

With the inner liner 17 in place the next step is to install thediaphragm 19. The diaphragm preferably is made of the same laminate asthe liners l7 and 23 and is sufficiently large so that it extends pasttheir flanges 17a and 23a. It is provided with a series of openingsabout its periphery which fit around a corresponding plurality of bolts67. By means of retaining strips of the same type as the retainingstrips 56 used for the liners 17 and 23 the edges of the diaphragm 19are sealed to the top surface of the concrete ring 25 so that the ringprovides a seal between the double walled insulating bucket formed bythe inner and outer liners l7 and 23 on the one hand and the diaphragm19 on the other hand.

Preferably, a fiberglass cushion 71 about one inch thick (see FIG. 4) islaid on top of the diaphragm 19 to prevent it from rubbing against thenet 29 which is next in the order of installation. Specifically, a net29 of steel cables is stretched across the concrete ring 25. in theexemplary embodiment disclosed particularly in FIGS. 1 and 5, the net 29is comprised of an outer steel l-beam ring 72, an inner steel ring 74,and a plurality of steel cables 73 stretched radially between them. Theentire net 29 can be assembled away from the tank and lowered in onepiece by a crane to rest upon the horizontal ledge of the concrete ring25, where it would then be bolted, to prevent it from rising thereafter.Thermal insulation 76 in loose form is installed around the edge of thenet 29 to prevent heat leaks between the ceiling insulation 31 and thewall insulation 21. Suitable tensioning devices 79 are usually providednear the end of the cables to give them a desired catenary. A layer ofscreening 81 is installed on top of the net 29 to provide a continuousfloor upon which the thermal insulating ceiling can be stacked. Toprovide a moisture-impervious protective layer for the thermal ceilinginsulation 31, a liner 85 which may be of the same construction as theliners 17 and 23 is next installed on top of the screening 79. Then,before the thermal insulation 31 is installed on top of the liner 85, aflange 87 is first formed through the liner 85, the screening 81, thefiberglass padding 71, and the diaphragm 19 below by cutting a hole 88through them in order to accommodate the casing of the submersible pump37.

Under the hole 88 a gasket 89 is placed and immediately on top of thehole opposite the gasket 89 a double-flanged collar 91 is laid. Thegasket 89 and the collar 91 are fastened together by a set of bolts 93,thereby forming a vapor sealing flange 87 and sandwiching between themthe liner 85 and the diaphragm 19. The next step is to lower thesubmersible pump system 37 through the flange 87 just formed. A suitablesuch pumping system is manufactured by the Carter Pump Company of CostaMesa, California and is described in US. Pat. No. 3,369,7l issued to J.C. Carter. Since the pumping system is commercially available, it willnot be described herein in detail. Suffice it to say that it includes acasing 95 having a bottom portion 95a and a top portion 951) havingabutting flanges 99 and 100 which are clamped and sealed together.

The initial part in installing the pumping system 37 is to lower thecasing 95 through the flange 87 by means of a crane. The casing 95 islowered to a depth sufficient to bring its bottom close to but not incontact with the bottom of the storage tank. It is then fixed in placeupon the support structure 35, suitable brackets 102 being provided onthe casing 95 for this purpose, and its flanges 99 and 100 are bolted tothe top flange of the ceiling collar 91. Next, a submersible,electrically powered pump 105 is lowered in place to the bottom of thecasing 95 to rest on top of a foot valve assembly 107 whichautomatically opens in response to the pump 105 being seated thereon.Electric power is supplied to the pump 105 through an electric cable 109fed from a conduit 108. By means of a connecting member 103, which maybe either a pipe or a cable suspended from a cover plate 101 at the topof the casing 95, the pump 105 may be both lowered into place andsubsequently lifted and removed from the casing for repairs withoutunduly disrupting the operation of the storage tank. For this purposethe connecting member 103 is suspended from the cover plate 101 by meansof a hand crank 104 which, when turned, is operative to lift or lowerthe pump 105. The hand crank 104 is used only to lift the pumpsufi'lciently to close the valve assembly 107. When it is desired toentirely remove the pump 105 from the casing 95, the cover plate 101 isremoved and other means, such as a crane are used to pull the pump 105from the casing.

As described in greater detail in the referenced Carter patent,cryogenic fluid is pumped out of the storage tank through an inlet andoutlet pipe flange 110 which extends from the upper casing portion 95b.

At the same time that the pump casing 95 is installed, there is alsoinstalled in the ceiling of the tank a fill and vent assembly 113comprised of a flanged, vent pipe 114 and a liquid fill pipe 116supported within the vent pipe. This may be accomplished in a mannersimilar to the installation of the casing 95. ln particular, an opening112 is cut through the ceiling material and receives a gasket 1 11 and adouble flanged collar 118 which are fastened together by a set of bolts117. The vent pipe 114 extends up through the ceiling structure of thetank and is rigidly held in place by brackets 120 bolted to the supportstructure 35. The liquid fill pipe 116 also extends through the ceilingstructure and has at its bottom a splash plate 122 to disperse thecryogenic fluid being fed therethrough.

Once the pump assembly 37 and the fill and vent assembly 113 have beeninstalled through the ceiling structure, the thermal ceiling insulationmay be laid. This thermal insulation may be in the same form as thatused for insulating the floor and walls of the storage tank and istherefore shown in F I68. 2 and 7 as several layers of thermallyinsulating pillows 31. The insulating pillows 31 are laid over theentire ceiling on top of the liner 85 and are preferably packed to theedge of the concrete ring 25 as shown in FIG. 5. A second liner 121,which may be of the same material as the bottom ceiling liner 85 is theninstalled over the ceiling insulating pillows 119. The ceiling screening81, and the ceiling liners 85 and 121 are anchored at their peripheriesin a groove 82 which extends all around the top of the concrete ring 25.As shown in FIG. 5, the manner of attachment is similar to that used forthe tank diaphragm 19. In particular, the screening 81 and the liners 85and 121 are sandwiched together in the groove 82, with a sealant beingapplied under each of them, and they are clamped in the groove 82 bymeans of long arcuate strips 83 fastened down by bolts 84 and nuts 86distributed along the groove. Additional vapor seals 124 are providedsubsequently where the casing 95 and the pipe 113 penetrate the upperliner 121 and the ceiling 33. The two liners 85 and 121 together form amoisture-impervious barrier which fully encloses the ceiling insulatingpillows 119. The space between the liners will be purged with inert gas.

To protect the ceiling 27 from damage caused by the elements, it isadvisable to install a protective roof 33. This structure may be made ofa flexible, airtight commercially available material, such as vinylcoated nylon fastened at its edges to the outer periphery of theconcrete ring by a set of bolts 123 and washers 125. The protective roof33 may be inert gas supported by maintaining the pressure in the space127 below it at slightly above atmospheric.

Prior to filling the vessel with cryogenic fluid, a purging of the innervessel and insulated annular space between outer and inner liners 23 and17 with inerting gas is accomplished by introducing inerting gas, suchas nitrogen, into the inner vessel area first, and then into the annulusthrough the inlet 69, maintaining a higher pressure in the vessel thanin the annulus to avoid displacement of the inner liner 17 from theinsulated wall.

The filling of the tank may now begin. It will usually be done throughboth the fill pipe 116 and the pump housing 95. For this purpose, thepipe flange 110 of the housing 95 is connected to a source of cryogenicfluid as is the fill pipe 116. By means of suitable external pumps,cryogenic fluid will then be fed through the pipes 110 and 116. Thefeeding of the cryogenic fluid through the fill pipe 116 has theadvantage that the cryogenic fluid is dispersed by means of the splashplate 122 near the top of the tank, thus serving to condense some of therising flash and vapor which is always generated when cryogenic fluidsare transferred. At subsequent times when the level of the cryogenicfluid in the tank has diminished, additional cryogenic fluid may besupplied through the fill pipe 116. This may be done either while thesubmerged pump is inoperative or at the same time that cryogenic fluidis being withdrawn from the tank by means of the pump 105 through thepipe 110.

To summarize, what has been described in some detail has been apreferred method of constructing an underground storage tank forcryogenic fluid and a storage tank constructed by such a method. It willbe appreciated that a storage tank such as that described hassignificant advantages over storage tanks which have been constructedpreviously. Thus, for example, the use of thermal insulation packed inbags to form pillows solves the problem previously encountered bythermal insulation which had been implanted in the form of rigid bricks.

Another feature of the storage tank described herein was seen to be theuse of sufficient insulation to reduce the heat leak from thesurrounding earth into the storage tank to a low enough level so as toprevent the thickness of the frozen wall from expanding out of control.Instead, the storage tank of the present invention is so designed as torequire additional cooling by means of the freeze pipes which surroundthe storage tank in order to maintain the frozen earthen wall and floorwhich surround the storage tank at a desired thickness. in keeping withthis aspect of the invention, as mentioned previously, a cooling systemwhich preferably is comprised of a pair of cooling units 43 and 45 isprovided. As mentioned previously, and as shown in addition in FIG. 9,the outputs of the cooling units 43 and 45 are connected to the longpipes 39 and to the short pipes 41 respectively and the cooling unitsare operated in response to signals received from the wall and floortemperature sensors 47 and 49, so as to vary the rate at which theyremove heat from the refrigerant being circulated through the pipes.

The manner in which the cooling units 43 and 45 are controlled inresponse to the detected floor and wall temperatures may be varied.Thus, the temperature sensors 47 and 49 may be connected throughrespective wires to a common instrument panel near the cooling units 43and 45 and a human operator can increase or reduce the output of thecooling units 43 and 45 as deemed by him necessary to maintain thefrozen earthen wall and floor of the storage tank at a desired uniformthickness.

It is anticipated that the greatest heat leak into the tank will occurnear the surface so that in most instances, once the earthen walls ofthe tank have been frozen, it will only be necessary to operate thesmall cooling unit 45 and its associated short freeze pipes 41.

If it is desired to eliminate the human operator, the cooling system maybe made automatic by interposing a control unit 127 between thetemperature sensors 47 and 49 and the cooling units 43 and 45. Thedesign of a suitable control unit is well within the skill of personsacquainted with the art of automatic temperature control and will not bedescribed herein. It will be sufficient to understand that theelectrical outputs of the temperature sensors 47 and 49 will be appliedto the control unit 127 which in turn will apply suitable controlsignals, either electrical or mechanical, to the cooling units 43 and 45so as to maintain the thickness of the frozen earthen wall and floor ofthe storage tank at a predetermined level.

What has been described herein is a storage tank which can hold a verylarge quantity of cryogenic fluid, such as liquid natural gas, at aconsiderably lower cost than has been heretofore possible. This has beenachieved through the combination of a number of structural features,such as the provision of a permanently frozen opening in the earthssurface whose walls are maintained at a constant thickness to preventfrost heaving, through the packing of thermal insulation incryogenically stable porous bags, and through the sealing of such bagsin a double walled liner to form in essence an insulating bucket insidethe frozen opening. These and other features of the invention aredefined in the claims which follow.

What is claimed is:

1. In an underground storage tank for liquified gas comprising:

a. an opening in the earth s surface;

b. a moisture-impervious liner covering the floor and walls of saidopening;

c. a resilient, collapsible, liquid and gas impervious container insidesaid lined opening;

d. a layer of thermal insulation distributed between said container andsaid liner, said thermal insulation being sufficient to avoid frostheave of said storage tank due to heat loss from said floor and wallsinto said liquified gas;

e. a thermally insulated ceiling covering the top of said opening; and

f. means for maintaining the earthen wall and floor of said openingfrozen to a controlled thickness during use by selectively cooling saidfloor and walls.

2. The storage tank of claim 1 characterized further in that saidcontainer is comprised of at least one multilayer laminate having layersof aluminum and polyester.

3. The storage tank of claim 1 characterized further in that:

a. a concrete ring surrounds the lip of said opening;

and

b. said liner is suspended from said ring.

4. The storage tank of claim 1 characterized further in that saidinsulation is packed in bags made of a cryogenically stable, porousmaterial, and said bags are stacked upon the floor and along the wall ofsaid openmg.

5. The storage tank of claim 1 characterized further by means forholding upright those bags of insulation which are stacked along thewall of said openings.

6. The storage tank of claim 1 characterized further by a shelf ofcompressible material extending along the bottom of said wall on theinsulated floor of said opening to form an indentation in said containerwhich fills out under the weight of said liquified gas in said containerby partially compressing said shelf.

7. The storage tank of claim 1 characterized further in that saidthermally insulated ceiling is comprised of:

a. two moisture-impervious liners sealed at their edges and extendingacross the top of said opening; and

b. thermal insulation sandwiched between said two layers.

8. The storage tank of claim 1 characterized further in that said meansfor maintaining the earthen wall and floor of said opening frozen to adesired thickness are comprised of:

a. freeze pipes permanently installed in the floor and wall of saidopening; b. means for circulating a heat conducting liquid through saidfreeze pipes; and c. means for removing heat from said circulated liquidl. prior to the operation of said storage tank to freeze said floor andwalls. and

2. during the operation of said storage tank to maintain said frozenfloor and walls at a desired thickness.

9. The storage tank of claim 8 characterized further y a. temperatureprobes placed in the earth around said opening for indicating thecondition of said floor and wall; and

b. means responsive to said temperature probes for controlling the rateat which heat is removed from said liquid so as to maintain the frozenfloor and wall of said opening at a desired thickness.

10. The storage tank of claim 1 characterized further in that saidcontainer is comprised of:

a. a laminate body in the shape of an inverted hat having a radiallyextending flange at its top; and

b. a laminate disk-shaped lid sized to reach substantially to the outerperimeter of said flange.

ll. The storage tank of claim 10 characterized further in that:

a. a concrete ring surrounds the lip of said opening;

and

b. the body-flange and lid of said container are both anchored upon saidring.

12. An underground storage tank for liquified gas comprising:

a. an opening in the earths surface, having an earthen floor and wallkept frozen during use by a cooling system having freeze pipes embeddedin said floor and wall;

b. a container conforming when filled to the shape of said opening;

c. thermal insulation means distributed between said container and thefloor and wall of said opening for limiting the heat loss from saidfloor and wall into said liquified gas to a sufficient extent to allowsaid cooling system to control the freezing of said earthen floor andwall; and

d. a thermally insulated ceiling covering the top of said opening.

13. An underground storage tank for liquified gas comprising:

a. An opening in the earth's surface, having an earthen floor and wallkept frozen during use by a cooling system having freeze pipes embeddedin said floor and wall;

b. A container conforming when filled to the shape of said opening saidcontainer comprised of:

a. a buckebshaped laminate body having a radially extending flange atits top; and

b. a laminate disk-shaped lid sized to reach substantially to the outerperimeter of said flange and bonded thereto;

c. thermal insulation means distributed between said container and thefloor and wall of said opening for limiting the heat loss from saidfloor and wall into said liquified gas to a sufficient extent to allowsaid cooling system to control the freezing of said earthen floor andwall.

14. An underground storage tank for liquified gas comprising:

a. An opening in the earth's surface,having an earthen floor and wallkept frozen during use by a cooling system having freeze pipes embeddedin said floor and wall;

b. A concrete ring surrounding the lip of said openc. A containerconforming when filled to the shape of said opening; said containercomprised of:

l. a bucket-shaped laminate body having a radially extending flange atits top, said body attached to and supported by said concrete ring, and

2. a laminate disk-shaped lid sized to reach substantially the outerperimeter of said flange said lid attached to and supported by saidconcrete ring.

15. For use in storing liquified gas in a bucket-shaped opening in theearths surface a thermally insulated container comprising:

a. a sealed, double walled, liquid and gas impervious bucket-shapedliner covering the floor and wall of said opening, and having a rim atits top;

b. thermal insulation packed in porous bags and distributed in acontinuous layer between the inner and outer walls of said liner;

c. a liquid and gas impervious diaphragm stretched across the mouth ofsaid opening and sealed to the rim of said liner; and

d. thermal insulation distributed in a continuous layer above saiddiaphragm.

16. For use in storing liquified gas in a bucket-shaped opening in theearth's surface a thermally insulated container comprising:

a. a sealed, double walled, liquid and gas impervious bucket-shapedliner covering the floor and wall of said opening, and having a rim atits top;

b. thermal insulation packed in porous bags and distributed in acontinuous layer between the inner and outer walls of said liner;

c. a reinforcing screen surrounding the inner wall of said liner; 5

d. a liquid and gas impervious diaphragm stretched across the mouth ofsaid opening and sealed to the rim of said liner; and

e. thermal insulation distributed in a continuous layer above saiddiaphragm.

1. In an underground storage tank for liquified gas comprising: a. anopening in the earth''s surface; b. a moisture-impervious liner coveringthe floor and walls of said opening; c. a resilient, collapsible, liquidand gas impervious container inside said lined opening; d. a layer ofthermal insulation distributed between said container and said liner,said thermal insulation being sufficient to avoid frost heave of saidstorage tank due to heat loss from said floor and walls into saidliquified gas; e. a thermally insulated ceiling covering the top of saidopening; and f. means for maintaining the earthen wall and floor of saidopening frozen to a controlled thickness during use by selectivelycooling said floor and walls.
 2. The storage tank of claim 1characterized further in that said container is comprised of at leastone multilayer laminate having layers of aluminum and polyester.
 2. alaminate disk-shaped lid sized to reach substantially the outerperimeter of said flange said lid attached to and supported by saidconcrete ring.
 2. during the operation of said storage tank to maintainsaid frozen floor and walls at a desired thickness.
 3. The storage tankof claim 1 characterized further in that: a. a concrete ring surroundsthe lip of said opening; and b. said liner is suspended from said ring.4. The storage tank of claim 1 characterized further in that saidinsulation is packed in bags made of a cryogenically stable, porousmaterial, and said bags are stacked upon the floor and along the wall ofsaid opening.
 5. The storage tank of claim 1 characterized further bymeans for holding upright those bags of insulation which are stackedalong the wall of said openings.
 6. The storage tank of claim 1characterized further by a shelf of compressible material extendingalong the bottom of said wall on the insulated floor of said opening toform an indentation in said container which fills out under the weightof said liquified gas in said container by partially compressing saidshelf.
 7. The storage tank of claim 1 characterized further in that saidthermally insulated ceiling is comprised of: a. two moisture-imperviouSliners sealed at their edges and extending across the top of saidopening; and b. thermal insulation sandwiched between said two layers.8. The storage tank of claim 1 characterized further in that said meansfor maintaining the earthen wall and floor of said opening frozen to adesired thickness are comprised of: a. freeze pipes permanentlyinstalled in the floor and wall of said opening; b. means forcirculating a heat conducting liquid through said freeze pipes; and c.means for removing heat from said circulated liquid
 9. The storage tankof claim 8 characterized further by: a. temperature probes placed in theearth around said opening for indicating the condition of said floor andwall; and b. means responsive to said temperature probes for controllingthe rate at which heat is removed from said liquid so as to maintain thefrozen floor and wall of said opening at a desired thickness.
 10. Thestorage tank of claim 1 characterized further in that said container iscomprised of: a. a laminate body in the shape of an inverted hat havinga radially extending flange at its top; and b. a laminate disk-shapedlid sized to reach substantially to the outer perimeter of said flange.11. The storage tank of claim 10 characterized further in that: a. aconcrete ring surrounds the lip of said opening; and b. the body-flangeand lid of said container are both anchored upon said ring.
 12. Anunderground storage tank for liquified gas comprising: a. an opening inthe earth''s surface, having an earthen floor and wall kept frozenduring use by a cooling system having freeze pipes embedded in saidfloor and wall; b. a container conforming when filled to the shape ofsaid opening; c. thermal insulation means distributed between saidcontainer and the floor and wall of said opening for limiting the heatloss from said floor and wall into said liquified gas to a sufficientextent to allow said cooling system to control the freezing of saidearthen floor and wall; and d. a thermally insulated ceiling coveringthe top of said opening.
 13. An underground storage tank for liquifiedgas comprising: a. An opening in the earth''s surface, having an earthenfloor and wall kept frozen during use by a cooling system having freezepipes embedded in said floor and wall; b. A container conforming whenfilled to the shape of said opening said container comprised of: a. abucket-shaped laminate body having a radially extending flange at itstop; and b. a laminate disk-shaped lid sized to reach substantially tothe outer perimeter of said flange and bonded thereto; c. thermalinsulation means distributed between said container and the floor andwall of said opening for limiting the heat loss from said floor and wallinto said liquified gas to a sufficient extent to allow said coolingsystem to control the freezing of said earthen floor and wall.
 14. Anunderground storage tank for liquified gas comprising: a. An opening inthe earth''s surface, having an earthen floor and wall kept frozenduring use by a cooling system having freeze pipes embedded in saidfloor and wall; b. A concrete ring surrounding the lip of said opening;c. A container conforming when filled to the shape of said opening; saidcontainer comprised of:
 15. For use in storing liquified gas in abucket-shaped opening in the earth''s surface a thermally insulatedcontainer comprising: a. A sealed, double walled, liquid and gasimpervious bucket-shaped liner covering the floor and wall of saidopening, and having a rim at its top; b. thermal insulation packed inporous bags and distributed in a continuous layer between the inner andouter walls of said liner; c. a liquid and gas impervious diaphragmstretched across the mouth of said opening and sealed to the rim of saidliner; and d. thermal insulation distributed in a continuous layer abovesaid diaphragm.
 16. For use in storing liquified gas in a bucket-shapedopening in the earth''s surface a thermally insulated containercomprising: a. a sealed, double walled, liquid and gas imperviousbucket-shaped liner covering the floor and wall of said opening, andhaving a rim at its top; b. thermal insulation packed in porous bags anddistributed in a continuous layer between the inner and outer walls ofsaid liner; c. a reinforcing screen surrounding the inner wall of saidliner; d. a liquid and gas impervious diaphragm stretched across themouth of said opening and sealed to the rim of said liner; and e.thermal insulation distributed in a continuous layer above saiddiaphragm.